During the course of well drilling operations, a wall of a wellbore being drilled is generally sealed and stabilized by means of a protective steel casing which is lowered through a borehole. Afterwards, the casing is cemented in place after retrieval of the drilling assembly. Setting a steel casing in a well is a time consuming and expensive procedure. To avoid substantial loss of time and expense, it is desired to minimize damage to a well casing during subsequent procedures for producing hydrocarbonaceous fluids from a formation such as high pressure well stimulation. Two such procedures comprise hydraulic fracturing and fracture acidizing. Deep well hydraulic fracturing and fracture acidizing frequently require surface pumping pressures near the burst pressure of a treating pipe or tubing. Usually, when high pressures are required, the tubing/casing annulus is pressurized to some lower pressure. This provides some support on the back side of the tubing. Water is a fluid generally utilized for pressurization along the tubing's back side.
However, there is some risk when using this technique. Should the tubing rupture, a substantial portion of the pressure in the tubing is transferred to the tubing/casing annulus. Since the larger diameter casing has a lower burst pressure than the tubing, catastrophic failure of the tubing may cause casing failure. Such casing failure will lead to extensive formation damage and expense in repairing said damage.
Therefore, what is needed is a method to prevent casing damage during high pressure well stimulation to avoid extensive down time and substantial expense.